The present invention relates generally to communication receiver systems, and in one embodiment, relates to paging systems which provide a plurality of information services to subscribing pager receivers. In such pager receivers, a particular information service is assigned to a particular capcode having a specified function state.
One widely used system for transmitting pager information is the POCSAG coding protocol for transmission of data which is illustrated in FIG. 1a. Data transmitted according to the POCSAG scheme consists of a preamble data stream followed by a plurality of data batches. The preamble data stream may be at least a 576 bit sequence of reversal bits, 010101 . . . 10, which is used to signal the pager to turn "on" and synchronize with the succeeding data batches. Each batch commences with a predetermined synchronization code S.sub.c followed by a plurality of data frames. Under the standard POCSAG scheme, there are eight frames per batch, and each pager receiver is assigned to a particular frame of each transmission batch. Each frame may be comprised of two codewords with each codeword having 32 bits of data.
The allocation of the bits under the POCSAG format is shown in FIG. 2. Under the POCSAG scheme, the first bit of the codeword is the Address/Message Flag 101 which identifies whether the codeword is an address codeword or a message codeword. If the Address/Message Flag is "0," the codeword is an address codeword, but when the flag is "1," the codeword is a message codeword. In an address codeword, the Address/Message Flag 101 is followed by address data 102 (bits 2-19), function data 103 (bits 20, 21), Bose, Chaudhuri and Hocquenghen (BCH) data 104 (bits 22-31), and an even parity bit 105 (bit 32). In a message codeword, the Address/Message Flag 106 is followed by message data 107 (bits 2-21), and error correction bits 108 (bits 22-32).
The two function bits 103 represent four function states with the combinations "00," "01," "10" and "11." The BCH bits 104 serve to correct errors that arise during the transmission of the address data. For instance, incomplete demodulation may result in an error. Thereafter, the even parity bit 105 further serves as an error check by representing whether the total number of "1"s from the start bit to the end bit correspond to an odd or even number.
In pager receivers using the POCSAG transmission format, each pager has at least one capcode or self call number which is an identification number assigned to the pager. Capcodes are stored in capcode slots in the pager's capcode memory (i.e., a first capcode is stored in capcode slot number 1, a second in slot number 2, etc.). The capcode number determines which frame of a batch will be read by the pager, and if there are multiple capcodes for a given pager, all capcodes must use the same frame.
Upon detection of the preamble and synchronization codeword, the pager turns "on" at its designated frame and demodulates the incoming radio signal into a data stream (see FIG. 1b). When, as shown in FIG. 2, the first codeword of the data stream is an address codeword 110 (because the Address/Message Flag 101 is set to "0"), the capcode or capcodes are retrieved from the pager memory for comparison to the address data 102 (i.e., bits 2-19). If none of the stored capcodes match or coincide with the address data 102, the pager 100 turns "off" for a predetermined amount of time and no further data is read. However, if one of the stored capcodes matches with the received address data 102, the pager 100 recognizes that it has been designated to receive additional information, and the pager 100 remains "on" to receive additional data. It will be understood that "matching" as used herein refers not only to strict one-to-one identity, but also to broader types of correspondence, including look-up tables, and other comparison means.
According to the POCSAG format, the next data to be received by the pager is the function data 103 (bits 20, 21) which represent four different function states (i.e., Functions A, B, C and D) associated with a particular capcode. The function bits 103 can be used to indicate a display mode or an alert mode.
Pagers in normal operation will turn "on" at the designated frame to receive address data 102 and, upon detection of coincidence between the address data 102 and one of the storage capcodes, will receive and process message data 107 contained in succeeding message codewords 109 (i.e., codewords having an Address/Message Flag 106 set to "1"). Thus, if numeric message data 107 is to be transmitted to a particular pager 100, an address codeword 110 is transmitted with address data 102 corresponding to the pager's capcode and with function data 103 indicating, for example, the type of alert. Thereafter, a message codeword 109 or sequence of message codewords is transmitted with numeric message data 107 contained in bits 2-21. This message data 107 is processed by the pager 100 and stored in a message memory for possible display to the subscriber. The subscriber would be notified of the presence of new information in the pager memory by an alert or other means as set by the function data in the address codeword. Upon completion of the transmission of message data, the pager turns off, but is periodically turned on to detect preamble data.
One of the advantages of the POCSAG protocol is reduced power consumption and extended battery life resulting from the pager power supply being kept on only when necessary. As seen in FIG. 1b, after turning "on" in response to the preamble data stream, the pager turns "on" only to read the synchronization codeword S.sub.c and one of the eight frames in each batch, but is otherwise turned "off." The designated frame for a pager is determined by the capcode number or numbers stored in the pager. After synchronization, the pager turns "on" at its designated frame to determine whether any detected address data matches with or is identical to the pager's stored capcode. If not, the pager turns off the power supply for a predetermined amount of time and no further data is processed.
A common feature on many pagers is the standard maildrop feature whereby message data is sent to a particular pager under address data which matches with the pager's maildrop capcode. Any message sent to a maildrop capcode is stored in a maildrop memory area, and any subsequent messages sent to that same maildrop capcode will completely overwrite and replace any previously-stored maildrop messages. Thus, if any messages containing only slight modifications (such as updated stock quotations) are to be sent, they must be retransmitted in their entirety so that any previous maildrop message can be completely replaced.
While the use of the POCSAG transmission scheme in pager systems is well known in the art, any changes in or additions to the pager services for a particular pager receiver require that the subscriber bring the pager unit "in shop" for reprogramming. This results in inconvenience not only to the subscriber who must bring the pager unit in for servicing, but also to the provider of paging service information who cannot add services or terminate services which have not been paid for until the pager unit is brought "in shop."
In addition, a certain amount of inefficiency is associated with conventional pager systems in that lengthy message texts with only minor alterations must be retransmitted in their entirety to each frame of the POCSAG signalling system, thereby consuming valuable air time for the transmission of "old" information.
The present invention sets forth a system for remote programming of a communication receiver which enables the provider of pager information services to program the pager unit over the air, and further enables the efficient transmission of message text information.